Bani Gajra

In memorium: Professor Arun Kumar Sharma

On 12th June 2017, Professor Arun Kumar Sharma, Founder Editor in Chief of The Nucleus presided over the Annual General Meeting with his usual poise and grace. Little did any one present could believe that it would be his last meeting. Five days later, he had an ischemic stroke and was admitted to a hospital. In the following 2 weeks it appeared that he would recover but his condition deteriorated on 6th July 2017, and he breathed his last around 20:30 h leaving his students, colleagues and admirers in deep anguish. His last journey was organized by the management of Ramakrishna Mission, Belur Math, Howrah and Ramakrishna Mission Institute of Culture, Golpark, Kolkata on 7th July amidst the chanting of Vedic hymns by the reverend Maharajs of Ramakrishna Mission Institute of Culture, Golpark, Kolkata where he was living during past few years. & Umesh C. Lavania lavaniauc@yahoo.co.in

Chromosome Information Service (CIS), XXXIl

Chromosome Information Service (CIS), XXXIl

Chromosome Information Service (CIS), XXIV

Genome duplication requires the coordinated action of multiple proteins to ensure a fast replication with high fidelity. These factors form a complex called the Replisome, which is assembled onto the DNA duplex to promote its unwinding and to catalyze the polymerization of two new strands. Key constituents of the Replisome are the Cdc45-Mcm2-7-GINS helicase and the And1-Claspin-Tipin-Tim1 complex, which coordinate DNA unwinding with polymerase alpha-, delta-, and epsilondependent DNA polymerization. These factors encounter numerous obstacles, such as endogenous DNA lesions leading to template breakage and complex structures arising from intrinsic features of specific DNA sequences. To overcome these roadblocks, homologous recombination DNA repair factors, such as Rad51 and the Mre11-Rad50-Nbs1 complex, are required to ensure complete and faithful replication. Consistent with this notion, many of the genes involved in this process result in lethal phenotypes when inactivated in organisms with complex and large genomes. Here, the authors summarize the architectural and functional properties of the Replisome and propose a unified view of DNA replication and repair processes.

Chromosome Information Service (CIS), XVIII

Chromosome Information Service (CIS), XXIX

Chromosome Information Service (CIS), XVI

Male meiosis and pollen fertility studies have been performed in 35 species belonging to 25 genera and 13 families of Polypetalae from the Dalhousie hills. Impatiens laxiflora (n= 6) was counted chromosomally for the first time. Corydalis cornuta (n=8), Erysimum hieracifolum (n=16), Arenaria serpyllifolia (n=10), Drymaria diandra (n=13), Geranium lucidum (n=14), Nasturtium officinale (n=16), Geum roylei (n=21) and Chaerophyllum reflexum (n=11) are worked out chromosomally for the first time in India. New cytotypes are recorded for Thalictrum saniculiforme (n=14), Drymaria diandra (n=13), Geranium lucidum (n=14) and Chaerophyllum reflexum (n=11). Present chromosome counts for the rest of the species substantiate earlier reports by other researchers. Intraspecific diploid (n=12) and tetraploid (n= 24) cytotypes recorded presently from Dalhousie hills in Oxalis corniculata are morphologically indistinguishable. The phenomenon of cytomixis involving inter PMC (pollen mother cell) migration of chromatin material has been observed in Ranunculus diffusus (n=16), Thalictrum foliolosum (n=7), T. saniculiforme (n=14), Gypsophila cerastioides (n=15), Oxalis corniculata (n=24), Murraya koenigii (n=9), Geum roylei (n=21), Potentilla atrisanguinea (n=21) and Pimpinella diversifolia (n=9). Cytomixis in these species results in various meiotic abnormalities and heterogeneous sized pollen grains. In the remaining species, the meiosis is normal, leading to high pollen fertility.

Chromosome Information Service (CIS), XIV

Four specific forces (H-bonds, van der Waals forces, hydrophobic and charge interactions) shape the structure of proteins, and many biologists assume they will determine the shape of all structures in the cell. However, as the mass and contour length of a human chromosome are ∼7 orders of magnitude larger than those of a typical protein, additional forces can become significant. The authors review evidence that additional non-specific (entropic) forces are major determinants of chromosomal shape and position. They are sufficient to drive the segregation (de-mixing) of newly replicated DNA to the poles of bacterial cells, while an entropic centrifuge can both form human chromosomes into territories and position them appropriately in nuclei; more locally, a depletion attraction can loop bacterial and human genomes.